Gluon-induced QCD corrections to pp --> ZZ --> l anti-l l' anti-l'

TL;DR

Problem: Higgs searches in H -> ZZ require precise background modeling, including loop-induced gg -> ZZ processes. Approach: complete calculation of gg -> Z*(gamma*)Z*(gamma*) -> 4 leptons using tensor reduction methods and multi-channel Monte Carlo, including gamma contributions and off-shell effects. Findings: gg channel yields about 14–15% correction to NLO qqbar background, with photon contributions significant below the ZZ threshold; the gg contribution has ~20% scale uncertainty while qqbar NLO has ~4%. Significance: results imply the full gg-induced background must be included for reliable Higgs discovery potential in pp -> H -> ZZ, particularly for M_H < 2 M_Z.

Abstract

A calculation of the loop-induced gluon-fusion process gg --> Z(photon)Z(photon) --> l anti-l l' anti-l' is presented, which provides an important background for Higgs boson searches in the H --> ZZ channel at the LHC. We find that the photon contribution is important for Higgs masses below the Z-pair threshold and that the gg-induced process yields a correction of about 15% relative to the NLO QCD prediction for the q anti-q-induced process when only a M(l anti-l), M(l' anti-l') > 5 GeV cut is applied.

Figures (1)

• Figure 1: Distribution in the $\ell\bar{\ell}\ell'\bar{\ell'}$ invariant mass $M_{4l}$ for the gluon scattering process $gg \to Z^\ast(\gamma^\ast)Z^\ast(\gamma^\ast) \to \ell\bar{\ell}\ell'\bar{\ell'}$ at the LHC with $Z^\ast Z^\ast$ contribution only (dashed) and all contributions (solid). Other details as in Table \ref{['kauer_nikolas_tbl:xsec']}.